1. Field of Invention
The present invention relates to a build-up suppressant having the following formula (I) used for suppressing the formation of a build-up during the polymerization reaction of vinyl halide or vinyl monomers having aromatic group(s) and causes many serious problems: ##STR1## in which, p denotes 1 or 2,
X and Y independently of one another represent hydrogen, C.sub.1 -C.sub.4 alkyl or C.sub.1 -C.sub.4 alkoxy, PA1 M represents hydrogen, or alkali metal or alkaline earth metal ion, PA1 R represents hydrogen or C.sub.1 -C.sub.3 alkyl, and PA1 X and Y independently of one another represent hydrogen, C.sub.1 -C.sub.4 alkyl or C.sub.1 -C.sub.4 alkoxy, PA1 M represents hydrogen, or alkali metal or alkaline earth metal ion, PA1 R represents hydrogen or C.sub.1 -C.sub.3 alkyl, and PA1 M' represents alkali metal or alkaline earth metal ion,
the number average molecular weight (M.sub.n) of the above build-up suppresant is 1000 or more.
The present invention also relates to a process for preparing the build-up suppressant of the above formula (I), a method for suppressing the build-up formation by coating the internal surface of a polymerization reactor with the build-up suppressant and to a method for polymerization of vinyl halide or vinyl monomers having aromatic group(s) in the above reactor internally coated.
2. Background Art
When vinyl chloride is homo- or copolymerized in aqueous suspension in a reactor, it has been well known that a problem arises in that metallic surface inside the polymerization reactor becomes coated with tenaciously adhering polymeric material known as build-up. The formation of tenaciously adhering build-up is undesirable from the view point of achieving efficient heat transfer and of lowering the stability of the processes. In addition, the build-up is causative of impurities or fish eye formation and thus lowers the polymer quality.
Hitherto, in order to solve such problems as mentioned above, the polymerization reactor has been cleaned between each polymerization cycle wherein the deposited materials are removed by hand cleaning or by pressurized water-washing. However, these methods are wasteful because they may induce an increment of cost and loss of productivity.
Therefore, many products having build-up suppressant activity have been studied from the view point of inhibiting the formation of the build-up itself (see Japanese Laid-open Patent Publication cation No. 56-78388 and European Patent Publication No. 52,421).
The Japanese Laid-open Patent Publication No. 56-78388 discloses a product having build-up suppressant activity produced by the condensation of aromatic aldehyde and phenol. But, since this build-up suppressant has a high solubility in monomer phase or medium phase, it may be solubilized into the reaction solution during polymerization and as a result, not only does not satisfactorily perform its function but also may act as an, impurity. Further, lowering of the build-up suppressant activity can occur in case where alkaline or aqueous mediums, or aqueous initiators are used during the reaction. Even though the cross-link was introduced therein, the build-up suppressant has not been improved in its activity. Moreover, it may cause a problem of environmental contamination due to an increment of the COD (chemical oxygen demand) in discharged waste water, and it may also worsen the working conditions because organic solvents such as methanol, ethanol, dimethylformamide (DMF) or ethyl acetate are used for preparing the build-up suppressant coating solution.
On the other hand, the European Patent Publication No. 52,421 discloses an aqueous product having good build-up suppressant activity formable by the condensation of 1-naphthol and formaldehyde, and a process for the preparation thereof. However, since this condensate is a low polymer such as cyclic trimer or tetramer, effect therefrom becomes unsatisfactory as may be solubilized into the reaction medium during polymerization reaction.
Accordingly, the present inventors have been extensively studied to develop a new build-up suppressant having much more effective suppressing activity than the earlier ones. The present inventors have focussed their attention on the chemical structure and molecular weight of the build-up suppressant, and consequently found an astonishing fact that such purpose can be satisfied by applying the condensate of formula (I) as a build-up suppressant to the reactor internal surfaces in the polymerization reaction of vinyl monomer, and thus completed the present invention.
Therefore, it is an object of the present invention to provide a novel build-up suppressant having the above formula (I) and a process for preparing the same.
It is another object of the present invention to provide a method for suppressing the build-up formation by coating the reactor internal surface with the build-up suppressant and a method for polymerization of vinyl halide or vinyl monomers having aromatic group(s) in the above reactor internally coated.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed to be merely illustrative of some of the more pertinent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a more thorough understanding of the invention may be had by referring to the disclosure of invention, in addition to the scope of the invention defined by the claims.